This invention relates to a semiconductor device having a construction in which circuit components inclusive of a switching semiconductor device are molded by a resin mold.
Power semiconductor devices of this kind are heretofore described in JP-B-3-63822 and JP-B-6-80748. A switching semiconductor device is set on a lead frame with spaces of a predetermined gap and this lead frame is in turn set to a heat sink made of a metal. A resin is packed for integral molding to the entire exterior portion inclusive of the spaces so as to constitute a semiconductor device. Because a resin layer is interposed between a conductor layer to which the semiconductor device is fixed and the heat sink in this construction, a plurality of semiconductor devices can be mounted, and because the number of components is small, reliability is high. Nonetheless, this construction is not free from the following items.
As described above, the method packs the resin to the spaces in which the devices are set in advance. Therefore, voids are likely to be entrapped at the time of molding and the thickness of the resin layer is likely to fluctuate. Generally, the heat transfer rate of the resin layer of this kind is extremely low and even a slight error of the layer thickness results in great variance of a thermal resistance. In consequence, stable quality cannot be obtained easily in mass-production plants. It is difficult for the same reason to lower the thermal resistance by markedly reducing the thickness of the insulating layer (to not greater than 0.1 mm, for example).
Another item resides in that because conductor wiring is constituted by the lead frame, miniaturization is difficult to attain. For instance, it is very difficult to form wiring having complicated and very fine shapes for mounting a microcomputer which is to control a driver IC, for example.